As the nation inches toward the fiscal cliff, two fresh dynamics are taking hold in Washington, both of which will be instructive as onlookers in Washington and financial players around the globe try to decipher if a deal is coming together or falling apart.

First, it’s clear that the center of gravity has moved toward the Senate, where there’s finally recognition on both sides of the aisle that Majority Leader Harry Reid (D-Nev.) and Minority Leader Mitch McConnell (R-Ky.) will likely have to craft and pass a bipartisan agreement before the Republican-controlled House takes it up. On Friday, though, all congressional leaders will meet at the White House.

This is an important stance, because Democrats claim Boehner can simply avert the fiscal cliff by passing a bill that would sneak through the Senate and garner most of the 191 Democrats in the House and a sliver of his GOP colleagues. Aiming to craft something that most of the 241 Republicans can support would help keep Boehner’s flank intact and weaken his dissenters.

Boehner was also unmoved by Treasury Secretary Timothy Geithner’s warning that the nation will reach its debt limit on Monday. Congress still has until February or March, Boehner told House Republicans on the call.

So there’s fresh sense of urgency, as raising the nation’s borrowing cap is still unlikely to be included in a final package.

But make no mistake: This is mostly theatrics, not real movement toward a bipartisan deal. Top aides involved in fiscal cliff discussions still say the chances of crafting a compromise and passing it through both chambers before Dec. 31 are well below 50 percent. Reid opened the day saying it “looks like” the nation was careening off the fiscal cliff.

And Washington has now accepted that a small, pared-back package — not a big deficit reduction measure that Obama and Boehner have been working on for weeks — is all that’s possible.

Right now, Democrats say Congress should extend current tax rates for income below $250,000. Republicans are privately saying they would like to see Democrats move closer to $500,000.

But even as these figures are tossed around, key individuals involved in crafting a compromise are hesitant to project what it might look like, because the chances of success are so remote.

There are two limiting elements at play: time and dramatic policy differences.

There are just four days until the end of the year.

This week, the Senate is working to help repair the damage wrought by Hurricane Sandy and to update the Foreign Intelligence Surveillance Act.

The House votes at 6:30 p.m. Sunday and then will enter into a closed party meeting at 9 a.m. Monday to talk fiscal cliff strategy. So the House won’t have any vote on a deal until Monday after 10 a.m. at the earliest.

If the Senate moves quickly to pass something over the weekend, the House could potentially pass it Dec. 31. But that would assume the procedural hurdles that typically slow the upper chamber are swept away.

Then Boehner has to get his House Republicans on his side.

The Ohio Republican was humiliated by the Plan B debacle last week, when he had to pull his proposal to raise taxes just on millionaires after failing to win support from his own GOP colleagues. In particular, Boehner was stymied by strong opposition from hard-line conservatives, many of whom refused to vote for any tax increase for any income group — even millionaires.

With virtually no support coming from Democrats, Boehner pulled the bill rather than risk a debilitating defeat. The House then adjourned for Christmas, leaving it unclear whether Boehner would even bring members back to Washington for the endgame of the fiscal cliff showdown.

But instead of moderating his position or seeking Democratic support for a compromise agreement, Boehner seems poised to move even further to the right, a potentially huge development heading into the 113th Congress.

With fights looming next year over boosting the $16.4 trillion debt limit and a potential government shutdown in late March, Democrats are now claiming that Boehner is more concerned about his own future — the Ohio Republican faces reelection as speaker on Jan. 3, the first day of the new Congress — than he is about solving the country’s budget woes.

Boehner is still trying to balance many competing, sometimes conflicting objectives. As a dealmaker himself, Boehner has signaled over and over again that he’s open to some kind of “grand bargain” with Obama and the Democrats.

But he has pulled back when such a deal has gotten close because he can’t trust his own majority. Unlike Democrat Nancy Pelosi of California or the Republican leader of yore, Newt Gingrich of Georgia, Boehner did not make his majority but instead shrewdly took advantage of the rise of the tea party movement — born out of opposition to Obamacare — to grab the speaker’s gavel.

However, not being one of these conservative upstarts himself has limited Boehner’s freedom to maneuver. Boehner thought he had gained additional authority by leading the House GOP majority through the 2012 elections but found that the leash was shorter than he thought.

Now, Boehner is indicating he may take a tougher line himself and let the chips fall where they may. That’s allowed Democrats to accuse him of putting internal House politics ahead of the nation — a claim his supporters staunchly deny.

“John Boehner seems to care more about keeping his speakership than keeping the nation on a firm financial footing,” Reid said on the Senate floor Thursday, launching his harshest verbal attack on Boehner since Election Day. “It’s obvious what’s going on. He’s waiting until Jan. 3 to get reelected to speaker because he has so many people over there that won’t follow what he wants.”